1. Field of the Invention
This invention relates to novel azo dyes and copper complex salts thereof, to water-soluble dye compositions containing them and to polarizing films containing an azo dye or copper complex salt dye of this invention adsorbed and oriented thereon as dichroic dyestuff and having high durability and a high polarization degree.
2. Description of the Related Art
It is now the common practice to produce a polarizing film by stretching a film of polyvinyl alcohol (PVA) or a derivative thereof or of a polyene and then causing iodine or a dichroic dye to be adsorbed as a polarizing element on the resulting oriented film.
Among such polarizing films, those making use of iodine as a polarizing element are excellent in initial polarizing performance but have poor resistance to water or heat. They are hence accompanied by a problem in durability when employed over a long period of time under high temperature and humidity conditions. To improve their durability, it is contemplated, for example, to enhance their treatment in an aqueous solution containing formaldehyde or boric acid or to use, as a protective film, a polymer film having low moisture permeability. Their durability is however still insufficient under high temperature and moisture conditions.
Polarizing films making use of a dichroic dye as a polarizing element have better durability against water and heat compared with polarizing films using iodine but are inferior in polarizing ability compared to the latter. With a view toward improving this drawback, polarizing films using an organic dye as a polarizing element with improved heat resistance and polarizing ability are proposed in Japanese Patent Laid-Open No. 313568/1989 [Chem. Absts. 112(24): 218407r] and Japanese Patent Laid-Open No. 12606/1991 [Chem. Absts. 115(4): 38339y]. When employed as polarizing films, such organic dyes are generally used in combination with a dye having absorption in a particular wavelength range to provide the polarizing films with a neutral color. It is therefore the current situation that depending on the dyes employed, such polarizing films may undergo a substantial color change at high temperatures.